BACKGROUND: To estimate the direct and indirect costs of severe asthma and the economic impact of its management to low-income families in Salvador, Brazil. METHODS: One hundred and ninety-seven patients with severe asthma and referred to a state-funded asthma center providing free treatment were evaluated. At registration, they were asked about family cost-events in the previous year and had a baseline assessment of lung function, symptoms and quality of life. During the subsequent year, they were reassessed prospectively. RESULTS: One hundred-eighty patients concluded a 12-month follow-up. Eighty-four percent were female patients, and the median family income was US$ 2955/year. Forty-seven percent of family members had lost their jobs because of asthma. Total cost of asthma management took 29% of family income. After proper treatment, asthma control scores improved by 50% and quality of life by 74%. The income of the families increased by US$ 711/year, as their members went back to work. The total cost of asthma to the families was reduced by a median US$ 789/family/year. Consequently, an annual surplus of US$ 1500/family became available. CONCLUSIONS: Family costs of severe asthma consumed over one-fourth of the family income of the underprivileged population in a middle-income country. Adequate management brings major economic benefit to individuals and families.